U.S. patent number 4,413,308 [Application Number 06/297,862] was granted by the patent office on 1983-11-01 for printed wiring board construction.
This patent grant is currently assigned to Bell Telephone Laboratories, Incorporated. Invention is credited to Vernon L. Brown.
United States Patent |
4,413,308 |
Brown |
November 1, 1983 |
Printed wiring board construction
Abstract
A mounting arrangement for an integrated circuit leadless chip
carrier (13) for providing compliance to prevent solder joint
failures due to stress and differential thermal expansion. A
supporting substrate board (10, 20, 30) has bonded to one surface a
flexible sheet (11) carrying printed wiring (12) to which the
carrier (13) is electrically connected by means of solder pedestals
(19). At each of the latter connections the board (10, 20, 30)
presents recesses (15, 22, 31a, 33a) over which the sheet (11) is
freely suspended to provide free sheet portions (18) which absorb
the stress and differential expansion to protect the solder
connections.
Inventors: |
Brown; Vernon L. (Boulder,
CO) |
Assignee: |
Bell Telephone Laboratories,
Incorporated (Murray Hill, NJ)
|
Family
ID: |
23148037 |
Appl.
No.: |
06/297,862 |
Filed: |
August 31, 1981 |
Current U.S.
Class: |
361/749; 257/734;
257/737; 361/764; 361/768; 361/776 |
Current CPC
Class: |
H05K
1/0271 (20130101); H05K 1/189 (20130101); H05K
1/05 (20130101); H05K 1/118 (20130101); H05K
1/182 (20130101); H05K 2201/2009 (20130101); H05K
3/0058 (20130101); H05K 3/3442 (20130101); H05K
2201/09109 (20130101); H05K 2201/10727 (20130101) |
Current International
Class: |
H05K
1/18 (20060101); H05K 1/02 (20060101); H05K
3/34 (20060101); H05K 3/00 (20060101); H05K
1/11 (20060101); H05K 1/05 (20060101); H05K
001/14 () |
Field of
Search: |
;361/398,399,401,403,421,408 ;357/70,80 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kucia; R. R.
Attorney, Agent or Firm: Kamstra; W. H.
Claims
What is claimed is:
1. A printed wiring board construction comprising an electrical
component having a pattern of electrical terminals thereon, a
supporting substrate having a planar surface having a recess
therein for each of said terminals and corresponding in position to
the positions of said terminals in said pattern of terminals, and a
flexible sheet carrying printed wiring affixed to said planar
surface extending over said recess for each of said terminals, said
sheet extending beneath the plane of said surface at said positions
of said terminals, said terminals being electrically connected to
said printed wiring within said recess for each of said
terminals.
2. A printed wiring board construction as claimed in claim 1, in
which each of said recesses is dimensioned larger than the
peripheral dimensions of each of said terminals and extends through
said supporting substrate.
3. A printed wiring board construction as claimed in claim 1, in
which each of said recesses is formed to conform to said pattern of
electrical terminals and extends partially in from said planar
surface.
4. A printed wiring board construction as claimed in claim 3 in
which said sheet is affixed to said substrate by an adhesive layer,
said planar surface being presented by the outer face of said layer
and in which said recesses are formed by an interruption in said
layer.
5. A printed wiring board construction as claimed in claim 3 in
which said electrical component comprises a leadless integrated
circuit chip carrier.
6. A printed wiring board construction as claimed in claim 5 in
which said electrical terminals are connected to said printed
wiring by solder connections.
7. A printed wiring board construction as claimed in claim 4 in
which said electrical component comprises a leadless integrated
circuit chip carrier.
8. A printed wiring board construction as claimed in claim 7 in
which said electrical terminals are connected to said printed
wiring by solder connections.
9. A printed wiring board construction comprising a supporting
substrate having a planar surface having a recess therein at each
of a plurality of component mounting locations, an electrical
component having a pattern of electrical terminals thereon for each
of said locations, and a flexible sheet carrying printed wiring
affixed to said planar surface extending over said recess at each
of said plurality of locations, said sheet extending beneath the
plane of said surface at said recess at each of said locations,
said terminals being electrically connected to said printed wiring
within said recess at each of said locations.
10. A printed wiring board construction as claimed in claim 9 in
which each of said recesses is dimensioned larger than the
peripheral dimensions of each of said electrical components and
extends through said supporting substrate.
11. A printed wiring board construction as claimed in claim 9 in
which each of said recesses is formed to conform to said pattern of
electrical terminals and extends partially in from said planar
surface.
12. A printed wiring board construction as claimed in claim 11 in
which said sheet is affixed to said substrate by an adhesive layer,
said planar surface being presented by the outer face of said layer
and in which said recesses are formed by an interruption in said
layer.
13. A printed wiring board construction as claimed in claim 11 in
which each of said electrical components comprises a leadless
integrated circuit chip carrier.
14. A printed wiring board construction as claimed in claim 13 in
which said electrical terminals are connected to said printed
wiring by solder connections.
15. A printed wiring board construction as claimed in claim 12 in
which each of said electrical components comprises a leadless
integrated circuit chip carrier.
16. A printed wiring board construction as claimed in claim 15 in
which said electrical terminals are connected to said printed
wiring by solder connections.
17. A printed wiring board construction comprising an electrical
component having a pattern of electrical terminals thereon, a
supporting substrate having a planar surface, said surface being
recessed at said pattern of terminals, and a flexible sheet
carrying printed wiring affixed to said planar surface, said sheet
extending slightly beneath the plane of said surface where said
surface is recessed, said pattern of electrical terminals being
electrically connected to said printed wiring where said sheet
extends beneath said plane of said surface.
Description
TECHNICAL FIELD
This invention relates to printed wiring board constructions and
particularly to arrangements for mounting thereon integrated
circuit chips and the like.
BACKGROUND OF THE INVENTION
Printed wiring boards with their mounted circuit components
together with their mounting frames are well known and have long
provided an advantageous means for assembling in an organized and
ordered fashion in an electronics system, large numbers of
electrical circuits. Generally, such boards have been adapted to
carry integrated circuit chips as well as larger circuit components
such as those referred to as dual, in-line circuit packs. In the
past, when circuit chips are to be mounted on the board, the chip
is first mounted on a chip carrier which is then electrically
connected to the board wiring, either by means of terminal pins
inserted in board sockets or by leads soldered to the board wiring.
The socket or leads provide the compliance necessary to prevent
solder joint failures which may result from excessive stresses
produced when the board is flexed either in manufacture or use, for
example. Such stresses may also be applied by the differential
expansion of the epoxy-glass board substrate and the ceramic
material of the chip carrier when the board assembly is temperature
cycled in normal use.
A conventional printed wiring board also presents varying degrees
of warp created either by manufacturing processes or as an inherent
characteristic of the board raw material. As a result, when a
warped, assembled printed wiring board is inserted in its mounting
frame, it may be forcibly straightened thereby causing relatively
large stresses to be applied to the electrical connections of the
components mounted on the board. Too, craftspersons may attempt the
manual straightening of a warped board before inserting it in its
frame, thereby bringing about the same stresses on the electrical
connections. In these circumstances, as one approach to the
problem, chip carrier leads and sockets have also, in the past,
provided the required compliance with these stresses to prevent
damage to the electrical connections.
Another approach to the compliance problem in the past has been to
apply a small pillar or pedestal of solder to each of the terminal
pads of the chip carrier. When the carrier is subsequently mounted
on the printed wiring board in a suitable solder flux and the
pillars reflowed, a solder connection is formed which is relied
upon to absorb the aforementioned stresses. This approach has its
own disadvantages. The control of the solder reflow required to
produce acceptable pillars has been difficult to achieve. The
application of the solder pillars also adds significantly to the
cost of the chip carrier. Further, because the melting point of the
solder is lower than the temperature required for the sealing
operation of the chip carrier, the solder application can only be
accomplished during device manufacture at some time after the
sealing operation. This adds further to the cost of the fabrication
of the chip carrier since completed batches of the carrier would be
discarded in the event of a single defective solder
application.
It is thus an objective of the printed wiring board construction of
the invention to provide a new and novel circuit chip mounting
arrangement for achieving stress compliance directed to the
foregoing and other problems.
SUMMARY OF THE INVENTION
The foregoing and other objectives are realized in one illustrative
integrated circuit chip mounting arrangement according to the
invention in which a circuit board is recessed at least in an area
where a solder connection is to be made between a chip carrier
terminal and the board printed wiring. The latter wiring is carried
by an insulative, flexible tape or sheet secured on the board by a
suitable adhesive and is permitted to dip slightly into the
recessed area or areas. At the chip carrier and wiring solder
connections, any differential stresses between the carrier and the
board occurring for whatever reason are absorbed by the flexible
circuitry at the connection points. For example, contraction or
expansion of the board simply causes a slight straightening or
further curvature, respectively, of the slack flexible circuitry
within the board recess or recesses. The possibility of solder
joint failures during handling or use of the board is thus
significantly reduced.
BRIEF DESCRIPTION OF THE DRAWING
The organization of an integrated circuit mounting arrangement
according to the principles of the invention together with its
features will be better understood from a consideration of the
detailed description of illustrative embodiments thereof which
follows when taken in conjunction with the accompanying drawing in
which:
FIG. 1 is an exploded, perspective view of a substrate board, a
flexible wiring overlay, and a number of representative integrated
circuit chip carriers which comprise components of the mounting
arrangement according to the invention;
FIG. 2 depicts an enlarged portion of the construction of FIG. 1 as
assembled as viewed from the rear of the latter figure;
FIG. 3 similarly depicts an enlarged portion of the construction of
FIG. 1 as assembled as viewed from the forefront of the latter
figure;
FIG. 4 is an enlarged section view of the construction portion
depicted in FIG. 2 taken along the line 4--4;
FIG. 5 is the same view as that of FIG. 4 with the difference that
an alternate manner of mounting a chip carrier is shown;
FIG. 6 is an enlarged section view of the construction portion
depicted in FIG. 3 taken along the line 6--6 in which portion
recesses are provided in the substrate board at the points of
carrier connections;
FIG. 7 is an enlarged section view of the mounting arrangement
according to the invention depicting an alternate means for
achieving the substrate board recesses shown in FIG. 6; and
FIG. 8 is an enlarged section view of the mounting arrangement
according to the invention depicting still another means for
achieving the substrate board recesses shown in FIG. 7.
DETAILED DESCRIPTION
Components of an illustrative integrated circuit chip carrier
mounting arrangement according to the invention shown in exploded
view in FIG. 1 include a substrate supporting board 10 of any
suitable hard material which here is assumed as metallic and a
flexible sheet 11 carrying various electrical conducting patterns
12 to which the chip carriers 13 ultimately will be electrically
connected. Chip carriers 13 are well known in the art as leadless
and are provided with rows of electrical terminals 14 arranged
about their peripheries on the underside. Carriers 13 are shown in
FIG. 1 as arranged in a representative pattern for their
connections to the conductors of flexible printed wiring sheet 11
at corresponding positions. At corresponding positions in
supporting board 10, a plurality of substantially rectangular
apertures 15 is presented, which apertures are dimensioned somewhat
larger than the outside dimensions of rectangular carriers 13. The
assembly and electrical interconnections of the components so far
considered are better seen from the enlarged portional view of FIG.
2 and the enlarged sectional view of FIG. 4. FIG. 2 shows a portion
of the assembly viewed from the rear of supporting board 10 showing
two representative chip carriers 13 in places within apertures 15
of board 10. The section view of FIG. 4 shows a portion of metallic
board 10 sectioned at an aperture 15. Board 10, in the illustrative
assembly being described, is faced on its exposed surfaces with an
insulative layer 16 and flexible printed wiring sheet 11 is affixed
to layer 16 across aperture 15 by means of a suitable adhesive
layer 17. In its span of aperture 15, sheet 11 is slightly offset
into aperture 15 as indicated by the exaggerated indentation in the
tape in FIG. 4 to present a slight rim 18 extending around and
within the periphery of aperture 15. In the embodiment of FIG. 4,
printed wiring 12 of sheet 11 is affixed thereon on its upper side
as viewed in the figure to which wiring the leadless terminals 14
of chip carriers 13 are electrically connected by means of solder
pedestals 19.
In FIG. 5 is shown an enlarged portion of the construction of the
invention substantially identical to that of FIG. 4 with the
difference that chip carrier 13 is mounted on the underside of
printed wiring sheet 11 as viewed in this figure, the same
reference characters being used to designate identical elements. In
either case, a thermal expansion or contraction of board 10 will
cause only a slight downward or upward displacement of carrier 13
within aperture 15 without placing strain on solder pedestals 19.
Thus, if thermal conditions cause a shrinkage of board 10, the
walls of aperture 15 will close slightly inward thereby causing a
contraction of sheet 11 which is taken up by the free rim 18.
Similarly, if board 10 expands, aperture 15 enlarges slightly,
causing sheet 11 to be stretched slightly across aperture 15 which
lengthening is again taken up by the free rim 18 of sheet 11. Any
warpage or bending of board 10 will also be absorbed by free rim 18
of sheet 11 to protect the solder connections.
In FIG. 3 and its enlarged section view of FIG. 6 is shown another
illustrative chip mounting arrangement according to the principles
of the invention in which recesses are provided in the supporting
board instead of complete apertures to achieve compliance. In FIG.
3, where the same reference characters are employed to designate
elements identical to those already described, a portion of a
printed wiring flexible sheet 11 is shown on a larger portion of
support board 20 to which sheet 11 is affixed by any suitable
adhesive. Board 20, like board 10 of the previous figures, is
formed of a suitable metallic material and is faced with an
insulative layer 21. Sheet 11 is affixed to the upper surface of
board 20 by means of a suitable adhesive layer 17 (FIG. 6) and chip
carrier 13 has its leadless terminals 14 again electrically
connected to the wiring 12 of sheet 11 by means of solder pedestals
19. Board 20 is again recessed at the latter connections but here,
as a variant of the novel arrangement of the invention, the recess
is provided only at the points of connection. Thus, for example, as
shown in FIG. 3, a rectangular channel 22 is presented in board 20
at each chip carrier location, the outer dimensions of channel 22
being somewhat larger than the outer dimensions of chip carrier 13.
Two legs 22a and 22b of channel 22 are shown enlarged in the
section view of FIG. 6. The width of channel 22 is determined so
that the chip carrier solder connections are made substantially
centrally in the width of the channel. As sheet 11 spans each leg
of rectangular channel 22 it is slightly depressed into the channel
to form two free sheet 11 portions about the entire channel, one on
each side of the carrier solder connections. Compliance is achieved
in the embodiments of FIGS. 3 and 6 in a manner identical to that
described for the embodiment of FIGS. 1, 2, 4, and 5. Any
differential change in the dimensions of chip carrier 13 and board
20 as well as strains due to handling are absorbed by the
aforementioned free sheet portions.
Another illustrative arrangement according to the invention for
achieving compliance in chip carrier mounting is shown only in the
enlarged portional section view of FIG. 7. In this arrangement, the
surface of metallic support board 30 remains even and a rectangular
channel, on leg 31a of which is shown, is formed by an interruption
of the required dimensions in the insulative layer 32 facing the
exposed surfaces of board 30. Printed wiring flexible sheet 11
secured to layer 32 by adhesive 17, spans the channel legs,
including leg 31a, again presenting free sheet portions for
providing compliance.
In FIG. 8 is shown still another arrangement for achieving a recess
across which the flexible sheet and its chip carrier connection may
be suspended. In this arrangement, depicted only in a portional
section view, supporting board 30 and its insulative layer 32
remain continuous and unbroken. A rectangular channel, one leg 33a
of which is shown, is formed by an interruption of the required
dimensions in a thicker layer 34 of the adhesive which bonds sheet
11 on the surface of board 30. The latter sheet spans the channel
legs to suspend the solder pedestals 19 thereacross, again
presenting free sheet portions for providing compliance.
As mentioned hereinbefore, the illustrative chip carrier
arrangements described may advantageously be employed to achieve
interconnection compliance on supporting boards on which other
electrical components such as dual in-line circuit packs are also
mounted. It will further be understood that what have been
described are considered to be only illustrative carrier mounting
arrangements according to the principles of the invention.
Accordingly, various and numerous other arrangements may be devised
by one skilled in the art without departing from the spirit and
scope of the invention as defined only by the accompanying
claims.
* * * * *